The present invention is directed to a magnetically-coupled actuating valve assembly for use in controlling an actuator, such as a hydraulic or pneumatic actuator. More specifically, the present invention is directed to an actuating valve assembly having a valve body that is magnetically coupled to a drive motor, thereby allowing the drive motor to be isolated from pressurized fluid passing through the valve assembly.
While it is to be understood that an actuator incorporating the actuating valve assembly of the present invention may be used in a variety of devices, the actuating valve assembly is particularly well-suited to use in an electronically controlled actuator for a prosthetic limb. More particularly, the valve assembly of the present invention is especially compatible with a damping cylinder of an electronically controlled prosthetic knee. Such a damping cylinder can be used to control (damp) the flexion and extension phases of knee movement during the gait cycle of an amputee.
Simple above-knee (AK) prostheses have been constructed with a hinged joint connecting a lower leg portion to an upper leg portion which, in turn, fits over the amputee's residual limb. Such a prosthetic limb allows the amputee to swing the lower leg portion forward during the extension portion of the gait cycle, and also allows for the lower leg portion to fold backward during the flexion portion of the gait cycle. Such simplistic artificial knee joints are problematic, however. For example, failure to fully swing the lower leg portion forward during the extension portion of the gait cycle can result in instability, as the knee joint may bend undesirably under the amputee's weight. In addition, the subsequent flexion of the joint relies solely on energy transfer from the gait cycle. Such knee joint operation can be very difficult for the amputee to control—especially as energy (and momentum) builds up during the gait cycle.
In an attempt to stabilize and control the gait cycle of an AK prosthetic limb, pneumatic and hydraulic damping cylinders have been utilized. These devices are used to damp energy generated during the gait cycle so that the prosthetic limb moves through its range of motion in a more controlled manner. Such damping cylinders can be designed and/or adjusted based on an amputee's weight, gait pattern, and activity level, among other factors. Prosthetic limbs employing such damping cylinders are an improvement over earlier limbs that used only undamped knee joints, however, they generally only allowed the amputee to walk well at one speed.
To further improve the performance of prosthetic limbs having damped knee joints, electronic control systems may be employed. These electronic control systems are in communication with a valve assembly or some other means of controlling the damping cylinder. For example, the valve assembly will typically employ a valve spool (body) or similar mechanism that interacts with various ports in the cylinder housing and allows for control over a flow of hydraulic or pneumatic fluid. A drive motor or some other type of actuator is generally used to shift the valve body or otherwise activate a flow control mechanism. The drive motor or other actuator may be located externally of the housing, or may be placed within the housing.
One problem with using such a valve assembly arises, however, due to the high working fluid pressures that are often present in the damping cylinder(s) that are controlled by the valve assemblies. For example, when locating a drive motor or other actuator externally to the housing, a connector, such as a shaft, must be provided to couple the actuator to the valve body. One or more seals must be located around the connector to prevent leakage of the working fluid to the outside of the cylinder. Because of the high working fluid pressures within the housing, these seals are prone to leakage, which can be quite problematic when the cylinder is used with a prosthetic limb. And, locating a drive motor or other powered actuator within the valve body does not overcome the aforementioned problem, as a seal must still be used around the wiring providing power thereto. Additionally, locating a drive motor in the working fluid generally results in reduced motor power and efficiency and, depending on the particular working fluid involved, may create a fire hazard.